A Voice for Our Earth: Scientists of the Intergovernmental Panel on Climate Change, 2014

“Many aspects of climate change and its associated impacts will continue for centuries, even if anthropogenic emissions of greenhouse gases are stopped. The risks of abrupt or irreversible changes increase as the magnitude of the warming increases.

…Surface temperatures will remain approximately constant at elevated levels for many centuries after a complete cessation of net anthropogenic CO2 emissions … A large fraction of anthropogenic climate change resulting from CO2 emissions is irreversible on a multi-century to millennial timescale, except in the case of a large net removal of CO2 from the atmosphere over a sustained period…

Shifting biomes, re-equilibrating soil carbon, ice sheets, ocean temperatures and associated sea level rise all have their own intrinsic long timescales that will result in ongoing changes for hundreds to thousands of years after global surface temperature has been stabilized.”

apollo08_earthrise
Image credit: NASA. Earthrise, an iconic photograph of our Earth taken from lunar orbit by Apollo 8 astronaut Bill Anders on December 24, 1968. The image was turned into a U.S. postage stamp in 1969 and has been called “the most influential environmental photograph ever taken.” It’s thought-provoking in that it provides a perspective on our Earth from the furthest away from it we humans have been. The moon in the foreground, and all other worlds in our solar system we have explored robotically, are interesting to study but display a striking lack of all the things we need to live when compared to our Earth. The nearest location of candidate worlds thought to have a chance at being suitable for civilization-scale life (without extensive geo-engineering) is over 4 light years away. (Meaning, according to our best understanding of physics, we could not possibly travel there in anything less than over 4 years, and that’s if we had the technology to travel the speed of light, which we don’t remotely.) Since it will likely take us at least hundreds of years to develop either the geo-engineering technology or the space travelling technology to provide a “Plan B” to our Earth, our planning for Earth’s continued ability to support our civilization must extend hundreds of years into the future. The text of this post describes the consensus scientific understanding that our actions right now will largely determine Earth’s ability to support us over that time frame. This is because we are applying a significant forcing (increasing atmospheric CO2) very quickly, geologically speaking, and our Earth’s systems are slow to fully respond. Forcing we apply now, even while the immediate effects may appear mild, will be irreversible and the effects will grow over time. With higher forcings, there are ever greater risks of encountering irreversible “tipping points” that could dramatically change our Earth’s climate in ways that are difficult or impossible to predict.

“Ocean acidification will continue for centuries if CO2 emissions continue, it will strongly affect marine ecosystems (high confidence), and the impact will be exacerbated by rising temperature extremes…

Global mean sea level rise will continue for many centuries beyond 2100 (virtually certain). The few available analyses that go beyond 2100 indicate sea level rise to be less than 1 m above the pre-industrial level by 2300 for [greenhouse gas] concentrations that peak and decline and remain below 500 ppm CO2-eq[uivalent]… For a radiative forcing that corresponds to a CO2-eq[uivalent] concentration in 2100 that is above 700 ppm but below 1500 ppm, … the projected rise is 1 m to more than 3 m by 2300 (medium confidence)… There is low confidence in the available models’ ability to project solid ice discharge from the Antarctic ice sheet. Hence, these models likely underestimate the Antarctica ice sheet contribution, resulting in an underestimation of projected sea level rise beyond 2100.

Sustained mass loss by ice sheets would cause larger sea level rise, and part of the mass loss might be irreversible. There is high confidence that sustained global mean warming greater than a threshold would lead to the near-complete loss of the Greenland ice sheet over a millennium or more, causing a sea level rise of up to 7 m. Current estimates indicate that the threshold is greater than about 1°C (low confidence) but less than about 4°C (medium confidence) of global warming with respect to pre-industrial temperatures. Abrupt and irreversible ice loss from a potential instability of marine-based sectors of the Antarctic ice sheet in response to climate forcing is possible, but current evidence and understanding is insufficient to make a quantitative assessment.

Within the 21st century, magnitudes and rates of climate change associated with medium to high emission scenarios … pose a high risk of abrupt and irreversible regional-scale change in the composition, structure and function of marine, terrestrial and freshwater ecosystems, including wetlands (medium confidence), as well as warm water coral reefs (high confidence). Examples that could substantially amplify climate change are the boreal-tundra Arctic system (medium confidence) and the Amazon forest (low confidence).  …A reduction in permafrost extent is virtually certain with continued rise in global temperatures.”

-Rajendra K. Pachauri (Chair), Myles R. Allen (United Kingdom), Vicente R. Barros (Argentina), John Broome (United Kingdom), Wolfgang Cramer (Germany/France), Renate Christ (Austria/WMO), John A. Church (Australia), Leon Clarke (USA), Qin Dahe (China), Purnamita Dasgupta (India), Navroz K. Dubash (India), Ottmar Edenhofer (Germany), Ismail Elgizouli (Sudan), Christopher B. Field (USA), Piers Forster (United Kingdom), Pierre Friedlingstein (United Kingdom/Belgium), Jan Fuglestvedt (Norway), Luis Gomez-Echeverri (Colombia), Stephane Hallegatte (France/World Bank), Gabriele Hegerl (United Kingdom/Germany), Mark Howden (Australia), Kejun Jiang (China), Blanca Jimenez Cisneros (Mexico/UNESCO), Vladimir Kattsov (Russian Federation), Hoesung Lee (Republic of Korea), Katharine J. Mach (USA), Jochem Marotzke (Germany), Michael D. Mastrandrea (USA), Leo Meyer (The Netherlands), Jan Minx (Germany), Yacob Mulugetta (Ethiopia), Karen O’Brien (Norway), Michael Oppenheimer (USA), Joy J. Pereira (Malaysia), Ramón Pichs-Madruga (Cuba), Gian-Kasper Plattner (Switzerland), Hans-Otto Pörtner (Germany), Scott B. Power (Australia), Benjamin Preston (USA), N.H. Ravindranath (India), Andy Reisinger (New Zealand), Keywan Riahi (Austria), Matilde Rusticucci (Argentina), Robert Scholes (South Africa), Kristin Seyboth (USA), Youba Sokona (Mali), Robert Stavins (USA), Thomas F. Stocker (Switzerland), Petra Tschakert (USA), Detlef van Vuuren (The Netherlands), Jean-Pascal van Ypersele (Belgium), Core Writing Team of the Intergovernmental Panel on Climate Change (IPCC) Synthesis Report, 2014.


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